The 2N3904 in breadboard test for first time

Thread Starter

lsepolis123

Joined Nov 21, 2020
3
BJT practice in breadboard

Bipolar transistors have three(3) poles, like The 2N3904 NPN
Middle pole is base?
The left/right poles are chosen arbitrarily,...? If No, how choose the collector?

Ground (-) what should be, and what (+)...?
 

LesJones

Joined Jan 8, 2017
3,176
Look at the datasheet for the device. To do that type 2N3904 datasheet into any search engine. (eg. Google )
For an NPN device the emitter will be connected to negative. (This may not be DIRECTLY. )

Les.
 

ScottWang

Joined Aug 23, 2012
7,024
When you facing the transistor number 2N3904 then you count it from left side, the 1 is Emitter, 2 is Base, 3 is Collector, the E normally connected to Ground, the B in series with a resistor and connected to the input signal or voltage, the C in series with a resistor and connected to +Vcc, and the output from C.
 

dl324

Joined Mar 30, 2015
12,871
Bipolar transistors have three(3) poles, like The 2N3904 NPN
Call them leads or pins, but not poles. I thought of frequency response when you mentioned poles.

2N, BC, and 2S transistors in TO-92 have different pin outs. 2N and BC are reversed from each other, but the middle lead is always the base. 2S have the base and emitter swapped from 2N.

2S pinout:
clipimage.jpg
 

Audioguru again

Joined Oct 21, 2019
3,186
Most little 2Nxxxx American transistor pins are EBC when viewed from the flat side. European BCxxx pins are the opposite, CBE.

I disagree with post #7 above. Oriental 2SCxxx little transistors usually have the C pin in the middle.
I found some 2SC945 Oriental little transistors with American and European pin locations so maybe they buy foreign transistors and re-label them?
 

Wolframore

Joined Jan 21, 2019
2,273
BJT practice in breadboard

Bipolar transistors have three(3) poles, like The 2N3904 NPN
Middle pole is base?
The left/right poles are chosen arbitrarily,...? If No, how choose the collector?

Ground (-) what should be, and what (+)...?
Since the BJT is made NPN or PNP we might be tempted to think of it as two diodes connected together. The base emitter junction is not the same as the base collector junction. The collector is normally bigger than the emitter.
1606044868431.jpeg
if you want to practice working with BJT I suggest starting with some circuits that you can observe. Perhaps a simple switch in saturation or a linear amplifier. Look for projects in books or online.

As the others have pointed out, always check the datasheet to understand which leads or pins are which. The 2N3904 is made by multiple manufacturers and the internal connections can vary.
 

dl324

Joined Mar 30, 2015
12,871
Since the BJT is made NPN or PNP we might be tempted to think of it as two diodes connected together.
Just say no...

I tried to use that line of thinking with a member who was having trouble with BJTs and it backfired. He started drawing transistors with two arrows and got even more confused. As I recall, a moderator and other members got on my case over it, but I never intended for the member to take it to that extreme.
 

Wolframore

Joined Jan 21, 2019
2,273
It’s a challenging concept and the dual diode model is inaccurate. You can’t just put two diodes back to back and call it a transistor. Sorry if that didn’t communicate. Hence the diagram that shows the difference in size. In reality it goes beyond that simple diagram.
 

dl324

Joined Mar 30, 2015
12,871
It’s a challenging concept and the dual diode model is inaccurate
The problem is that there are two PN junctions arranged in the orientation you'd draw, but they don't work like two diodes orientated in that manner. All analogies have shortcomings that can confuse newbies. My current position is to just bite the bullet and understand it the way they teach it in text books. That method worked for all (most?) of us who studied it in school.
 

Thread Starter

lsepolis123

Joined Nov 21, 2020
3
The Electronics Shop bought --- does Not know the supplier of this BJT 2N3904 NPN.
Does all 2N3904 NPN have the same positioned pins?
If yes, What is the standard?
If No, How to find this, with a Digital Multimeter...?
 

BobTPH

Joined Jun 5, 2013
3,315
The Electronics Shop bought --- does Not know the supplier of this BJT 2N3904 NPN.
Does all 2N3904 NPN have the same positioned pins?
Never seen one that didn’t have the normal pinout, and it would have a different part number if it did.

For example 2N2222 type transistors dio have different pinouts, but the actual part numbers are changed, 2N2222, PN2222 an P2N2222.

Bob
 

AnalogKid

Joined Aug 1, 2013
9,254
The left/right poles are chosen arbitrarily,...? If No, how choose the collector?
There are six possible combinations of pin assignments for a transistor in a TO-92 package, and ALL of them are used somewhere in the industry. There is no standard. Some are used much more often than others, but there is no way to be sure other than reading the datasheet for the *exact* part number you have.

I know it makes no sense and is frustrating. I've been dealing with it for over 50 years and it doesn't get any better.

ak
 

Audioguru again

Joined Oct 21, 2019
3,186
If your supplier does not know who made the transistors he sells (ebay?) then do not use the transistors and do not buy from that supplier.
Look at the part number of a transistor in Google. The listing for 2N3904 begins with the datasheet from ON Semi and many photos of the transistor from other Name-Brand manufactures showing which pin is which.
 

Wolframore

Joined Jan 21, 2019
2,273
Well you can narrow it down by using a multimeter to determine which is the base.

Check for the diode like this: As you already know a forward biased silicon diode will drop about 0.6-0.7V and will show as open if they're reversed.

1606593113149.png
 
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